Valve assemblies for dispensing or dosing small amounts of a fluid are known. However, high precision repeatable dispensing is hard to be achieved, due to the structural design of the valve as well as operational parameters of the fluid that may change during use.
In particular, four different variables can affect a precise and constant operation of a valve, these variables being:                Time of opening of the valve: this parameter depends on the valve design and becomes really critical when very small amounts of dispensed fluid are required, which means very short opening time of the valve;        Diameters of the inlet and outlet orifices of the valve: if such diameters are very small, it is important to machine such orifices with as high precision as possible;        Viscosity of the fluid being dispensed, which determines the ability of the fluid to flow through the fluid path and therefore the amount of fluid dispensed during the cycle of valve opening: depending on the nature of the fluid, its viscosity can vary with the ambient temperature;        Pressure of the fluid, which determines the force and resultant speed of the fluid through the fluid path: non constant pressure of the fluid being dispensed means variable amounts of fluid passing through the valve orifices.        
The above parameters are particularly critical when the fluid is a viscous fluid, such as a glue or a liquid adhesive.